Speaking the Same Language as a Wireless Thermometer

Temperature is a delicate thing. Our bodies have acclimated to a tight comfort band, so it is no wonder that we want to measure and control it accurately. Plus, heating and cooling are expensive. Measuring a single point in a dwelling may not be enough, especially if there are multiple controlled environments like a terrarium, pet enclosure, food storage, or just the garage in case the car needs to warm up. [Tim Leland] wanted to monitor commercially available sensors in several rooms of his house to track and send alerts.

The sensors of choice in this project are weather resistant and linked in his project page. Instead of connecting them to a black box, they are linked to a Raspberry Pi so your elaborate home automation schemes can commence. [Tim] learned how to speak the thermometer’s language from [Ray] who posted about it a few years ago.

The system worked well, but range from the receiver was only 10 feet. Thanks to some suggestions from his comments section, [Tim] switched the original 433MHz receiver for a superheterodyne version. Now the sensors can be a hundred feet from the hub. The upgraded receiver is also linked on his page.

We’ve delved into thermocouple reading recently, and we’ve featured [Tim Leland] and his 433MHz radios before.

Radiosondes: Getting Data from Upstairs

Ever since I first learned about radiosondes as a kid, I’ve been fascinated by them. To my young mind, the idea that weather bureaus around the world would routinely loft instrument-laden packages high into the atmosphere to measure temperature, pressure, and winds aloft seemed extravagant. And the idea that this telemetry package, having traveled halfway or more to space, could crash land in a field near my house so that I could recover it and take it apart, was an intoxicating thought.

I’ve spent a lot of time in the woods over the intervening years, but I’ve never seen a radiosonde in the wild. The closest I ever came was finding a balloon with a note saying it had been released by a bunch of schoolkids in Indiana. I was in Connecticut at the time, so that was pretty cool, but those shortsighted kids hadn’t put any electronics on their balloon, and they kind of left me hanging. So here’s a look at what radiosondes are, how they work, and what you can do to increase your chances of finding one.

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Old Thermometer Gets New Eyes

As much as we’d like to have the right tools for the right job all of the time, sometimes our parts drawers have other things in mind. After all, what’s better than buying a new tool than building one yourself from things you had lying around? That’s at least what [Saulius] must have been thinking when he needed a thermometer with a digital output, but only had a dumb, but feature-rich, thermometer on hand.

Luckily, [Saulius] had a webcam lying around as well as an old thermometer, and since the thermometer had a LCD display it was relatively straightforward to get the camera to recognize the digits in the thermometer’s display. This isn’t any old thermometer, either. It’s a four-channel thermometer with good resolution and a number of other useful features (with an obvious lack of communications abilities), so it’s not something that he could just overlook.

Once the camera was mounted to an arm and pointed at the thermometer’s screen, an algorithm running on a computer detects polygons and reports its information into a CSV file. This process is made simpler by the fact that LCD screens like this are very predictable. From there, the data is imported into LibreOffice and various charts and graphs can be made.

Although perhaps not the most elegant of hacks, sometimes you have to work with the supplies that are on hand at the time. Sometimes the tools you need are too expensive, politically dangerous, or too impractical to obtain. To that end [Saulius]’s hack is a great example of what hacks are possible with the right mindset.

Nixie Thermometer Destined for Custom PC Case

There’s no denying the retro appeal of the warm glow of a set of Nixies, and when a friend was looking for a unique touch for the case of his new liquid-cooled PC, [Luca] pitched in with this sweet Nixie thermometer.

From the look of [Luca]’s detailed blog entries, he’s been at this build since the New Year. He starts with a list of requirements, including the oddly specific need for a round PC board. For the thermometer, three Nixies are enlisted for the display, two for the temperature and one for the units. Everything was prototyped on perf board before committing to a PCB design, but even with careful planning, the Nixie sockets on the final PCB came out a tiny bit too close together. Luckily the tubes still fit, even if they are snuggled together some. And yes, the tube bases all include the hated RGB LEDs – hey, it’s what the customer wanted. The specs are for the colors to change at the touch of a button; we’d like to see a color gradient linked to the temperature – blue for “nice and cool”, red for “leave the room.” You can see the finished thermometer in action below the break.

The recent run of Nixie projects continues unabated, and this one has a nice look that’s sure to complement the finished case. We’ve asked [Luca] to keep us up-to-date on the project, so hopefully we’ll get a look at why a round PCB is needed. While we wait for that, check out an earlier Nixie thermometer build with a bar graph twist.

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BBQ Thermometers Get Serious

You can write with a fifty cent disposable pen. Or you can write with a $350 Montblanc. The words are the same, but many people will tell you there is something different about the Montblanc. Maybe that’s how [armin] feels about meat thermometers. His version uses a Raspberry Pi and has a lengthy feature list:

  • 8 Channel data logging
  • Plotting
  • Webcam (USB or Raspicam)
  • Alarms via a local beeper, Web, WhatsApp, or e-mail
  • Temperature and fan control using a PID
  • LCD display

You can even use a Pi Zero for a light version. There’s plenty of information on Hackaday.io, although the full details are only in German for the moment. As you can see in the video below, this isn’t your dollar store meat thermometer.

Even though a disposable pen does the same job as a Montblanc, most of us would rather have a Montblanc (although Hackday would have to hand out some pretty steep raises before we start using the Meisterstück Solitaire Blue Hour Skeleton 149).

We might have done more with an ESP8266 and then done more work on the client, but we have to admit, this is one feature-packed thermometer. We’ve seen simpler ones that use Bluetooth before, along with some hacks of commercial units.

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Vintage Microammeter Now Tells Temperature

[Craig] sent in this tip about a simple hack he built to convert an old analog micro-ammeter into a thermometer using a few parts. There’s a certain charm to retro analog meters, and there was enough space inside the old meter to accommodate the tiny breadboarded circuit and the three AA batteries to convert it into a cool looking centerpiece which is useful too!

He used the 3-pin MCP9700 analog temperature sensor connected to a LTC1541 – a combined comparator, op-amp and band gap reference voltage all rolled into one package. The thermometer displays 1uA per degree Celsius, has an output of 1mV per degree Celsius for external temperature monitoring / data logging, and draws just about 20uA. While the build itself is pretty simple, [Craig] took the time to walk through every design decision he made in the video after the break. This starts with the design for his circuit, and  moves on to the selection of parts and their values. The video is a must-watch for anyone wanting to learn more about precision op-amp based designs.

The three batteries will drain over time, and a circuit like this one requires a stable reference voltage. That is taken care by the bandgap reference voltage from the LTC1541. This eliminates the use of additional voltage regulators, and allows the circuit to work from 4.5V down to about 3.3V. Check the video after the break to listen to [Craig] describe how it works. We’re not sure how quickly it responds to changes in ambient temperature since the sensor is enclosed inside the meter, so maybe some vents at the back, or bringing out the sensor might be a good idea.

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Reverse-Engineering a Wireless BBQ Thermometer

[Bob] has his own smoker and loves to barbecue, but doesn’t like spending all day checking on his smoker’s temperature. He thought about building his own wireless thermometer setup, which would have been pretty awesome, but then he had a better idea: why not hack an existing wireless barbecue thermometer? [Bob] purchased an off-the-shelf wireless BBQ thermometer and reverse-engineered its wireless protocol to make his own wireless thermometer setup.

The first problem [Bob] encountered was figuring out the frequency of the transmitter. Thankfully [Bob] had access to a spectrum analyzer, where he discovered the transmitter was running at 433.92MHz (a cheap RTL-SDR dongle would also get the job done). Next, [Bob] started digging into the manufacturer’s FCC filings and found that it actually called out the transmit frequency, which matched the transmit frequency he measured. He also found a ton of other helpful information in the filing, like a block diagram and full transmitter schematic.

[Bob] used a Radiometrix RF module to receive the thermometer’s signal. He hooked up the output to his logic analyzer to start decoding the protocol. After a quick visual analysis, [Bob] found that the signal was a preamble followed 13 bytes of Manchester-encoded data being transmitted at 2kbps. He started collecting data with known temperatures, created a table of the data, and began looking for patterns. After quite a bit of searching [Bob] was successfully able to find and parse the temperature values out of the data stream. [Bob] did a great job of documenting his process and results, so check out his writeup if you want to try it out yourself.